The present invention relates to novel quaternary ammonium compounds, to a composition comprising such compounds and to methods and uses relating thereto.
In particular the present invention relates to the use of quaternary ammonium compounds as fuel or lubricant additives, especially as fuel additives and preferably as diesel fuel additives.
It is common to include nitrogen-containing detergent compounds in lubricating oil and fuel oil compositions in order to improve the performance of engines using such compositions. The inclusion of detergent additives prevents the fouling of moving parts of the engine. Without such additives fouling would cause the performance of the engine to diminish and eventually cease.
Many different types of quaternary ammonium salts are known in the art for use as detergent additives in fuel and lubricating oil compositions. Examples of such compounds are described in U.S. Pat. Nos. 4,171,959 and 7,951,211. One commonly used class of quaternary ammonium additives is prepared by the reaction of a tertiary amine with an epoxide and an acid. Various acids may be used but typically these are small acid molecules, for example acetic acid, and the counterion to the quaternary ammonium cation is not considered to be of importance.
Detergent additive compounds typically include a polar group and a hydrophobic group. The hydrophobic group is typically a long chain hydrocarbyl moiety. A common feature of existing quaternary ammonium salt detergent additives is that the hydrophobic group is included within the cationic portion of the compound. The present inventors have surprisingly found that quaternary ammonium salts including a hydrophobic moiety in the anion can provide good performance as a detergent even when a lower molecular weight cation is used. Furthermore the inventors have noted that use of diacid species as the anion is particularly beneficial.